Journal of Experimental Botany, Vol 50, 89-99, Copyright © 1999 by Oxford University Press
Z Cheng and K Bradford
Controlled hydration of seeds followed by drying (seed priming) is used to
break dormancy, speed germination, and improve uniformity of radicle
emergence. To date, empirical trials are used to predict optimal priming
conditions for a given seed lot. Since priming is based upon seed water
relations, it was hypothesized that the sensitivity of germination to
reduced water potential before priming might be mechanistically related to,
and therefore predictive of, priming responsiveness. Analyses of
germination of 13 tomato (Lycopersicon esculentum
Mill.) seed lots at two temperatures (15
ARTICLES
Hydrothermal time analysis of tomato seed germination responses to priming treatments
Department of Vegetable Crops, One Shields Avenue, University of California, Davis, CA 95616-8631, USA; Corresponding author; Fax: +1 530 752 4554; E-mail: kjbradford@ucdavis.edu
C
and 20C) and three water potentials (0,
-0.28 and -0.43 MPa) showed that seed lot germination responses could be
quantitatively characterized by parameters derived from thermal time,
hydrotime, and hydrothermal time models
(R2
0.73-0.99). Six of the seed
lots were primed at two temperatures (15°C and 20°C) and
three water potentials (-1.0, -1.5 and -2.0 MPa) for various durations,
dried, and their subsequent germination rates analysed according to
hydropriming time and hydrothermal priming time models. The responses of
germination rates to priming were characterized by hydropriming time
(
HP) and hydrothermal priming time (HTP) constants and
the minimum water potential (
min) and temperature
(Tmin) for achieving a priming effect. The values of
min and Tmin varied relatively little among
tomato seed lots, and the generalized values of min=2.39 MPa and
Tmin=9.10°C accounted for 74% (15°C),
57% (20°C), and 62% (across both temperatures) of the increase in
germination rates following priming. Nonetheless, while the hydrothermal
time models described germination patterns both before and after priming,
there was relatively little predictive relationship between
them.Keywords: Lycopersicon
esculentum Mill., tomato seeds, germination models, seed
priming, temperature, water potential.
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